The present invention relates to an improvement in an internal combustion engine ignition system and, more particularly, to the prevention of excessive engine revoltion speeds.
Since an internal combustion engine of the high power type is frequently run in a high r.p.m. range, there is a fear that the engine may break down if driven at an abnormally high r.p.m. For this reason, high power internal combustion engines are generally possessed of an excessive r.p.m. prevention function so that the engine r.p.m. may not exceed a predetermined value.
As one method of preventing excessivc r.p.m., it is known to temporarily interrupt the operations of the ignition system.
One system according to the prior art will be described in the following, with reference to FIGS. 1 and 2.
In FIG. 1, reference numeral 1 indicates an ignition signal generator for generating an ignition signal in accordance with the r.p.m. of the internal combustion engine. Indicated at numeral 2 is an ignition pulse circuit for processing the ignition signal from the ignition signal generator 1 to shape the waveform thereof and to control the dwell angle to thereby generate ignition pulses. Indicated at numeral 3 is a switching circuit for interrupting the power supply to a later-described ignition coil 4 in response to the ignition pulses from that ignition pulse circuit 2. The ignition coil 4 is equipped at one end with a power source terminal 5 for supplying electric power, and is adapted to be driven to generate an ignition voltage by the switching circuit 3. Indicated at numeral 6 is a pulse generator for generating a pulse signal of a predetermined time width in response to the ignition signal from the ignition signal generator 1. Indicated at numeral 7 is an FV converter which is made receptive of the pulse signal from the pulse generator 6 to generate a revolution information signal at a level proportional to the r.p.m. of the engine. The FV converter 7 may be constructed, for example, such that it charges or discharges a capacitor in response to the pulse signal from the pulse generator 6 to thereby generate a d.c. voltage at a level according to the engine r.p.m. at that time. Indicated at numeral 8 is a revolution detector for comparing the level of the revolution information signal from the FV converter 7 to generate an ignition interrupting pulse in synchronism with the ignition signal from the ignition signal generator 1 when the revolution information signal exceeds a reference level. Indicated at numeral 9 is a bypass circuit connected between the output terminal of the aforementioned ignition pulse circuit 2 and an earth potential and which is made operative to bypass the ignition pulses from the ignition pulse circuit to earth in response to the ignition interrupting pulse from the aforementioned revolution detector 8.
FIG. 2 is a waveform chart showing the operational waveforms of the respective units of FIG. 1. FIG. 2(A) shows the level-compared operational waveform of the revolution detector 8, and character a.sub.1 indicates a set reference voltage whereas character a.sub.2 indicates the revolution information signal from the FV converter 7. Moreover, FIG. 2(B) shows the waveforms of the ignition and interruption pulses of the output of the revolution detector 8.
An explanation of the operation of this device will be made in the following. First of all, the ignition operation will be described. The ignition signal generated by the ignition signal generator 1 in accordance with the r.p.m. of the internal combustion engine in fed to the ignition pulse circuit 2. This circuit shapes the waveform and controls the dwell angle of the ignition signal to thereby generate ignition pulses of a pulse width having such a proper dwell angle as accords with the the running state of the engine. The input pulses thus generated are fed to the switching circuit 3. The circuit controls the power supply to the ignition coil 4 in accordance with the ignition pulses. As a result, when the power supplied to the ignition coil 4 is interrupted, there is generated a high voltage at the secondary side of the ignition coil 4, by which the engine is ignited and run.
Next, the ignition interrupting operation will be described. The pulse generator 6 generates a pulse signal of a predetermined time width in response to the aforementioned ignition signal generated by the ignition signal generator 1. The resultant pulse signal is fed to the FV converter 7, by which it is converted into a revolution information signal at a level proportional to the engine r.p.m. This FV converter 7 may operate, for example, to charge or discharge a capacitor in accordance with the pulse signal from the pulse generator 6 thereby to generate a revolutional information signal having a d.c. voltage at a level according to the engine r.p.m. at that time. The revolution information signal has its level compared with the reference voltage by the revolution detector 8.
This comparing operation will now be described with reference to FIG. 2(A). Here, the reference voltage a.sub.1 is at a constant level whereas the revolutional information signal a.sub.2 is a signal at a level proportional to the engine r.p.m. such that it rises with a rise in engine r.p.m. The revolution information signal a.sub.2 exceeds the reference voltage a.sub.1 at a time t.sub.1. At this time, the revolution detector 8 generates an ignition interrupting pulse in synchronism with the aforementioned ignition signal, as is shown in FIG. 2(B). These ignition interrupting pulses are fed to the bypass circuit 9, which operates in accordance with the ignition interrupting pulses to thereby bypass the ignition pulses, normally fed from the ignition pulse circuit 2 to the switching circuit 3, to earth. As a result, the switching circuit 3 has no input so that its switching operation is interrupted to interrupt the control of the power supply to the ignition coil 4. As a result, no ignition voltage is generated at the output of the ignition coil 4 so that the engine is not fired but is brought into a misfiring state, in which its r.p.m. is reduced. As a result, the revolution information signal a.sub.2 drops until it becomes lower than the reference voltage a.sub.1. At this time t.sub.2, the revolution detector 8 ceases to generate the ignition interrupting pulses, and the bypass circuit 9 ceases its bypass function so that the ingition pulses from the ignition pulse circuit 2 are again fed to the switching circuit 3. As a result, this switching circuit reopens the power supply to the ignition coil 4 so that the ignition voltage is generated at the secondary side of the ignition coil 4 to cause ignition and run the engine.
Moreover, if the engine r.p.m. again rises until the aforementioned revolution information signal a.sub.2 again exceeds the reference voltage a.sub.1, the aforementioned ignition interrupting operations are repeated, as indicated at time t.sub.3 in FIG. 2(B). Thus, the engine r.p.m. is controlled on an average at a predetermined value by alternating igniting operations and ignition interrupting operations.
Here, since the aforementioned revolution detector 8 generates ignition interrupting pulses in synchronism with the ignition signal from the ignition signal generator 1, the bypass passage 9 has its operation blocked during power supply to the ignition coil 4 so that it is possible to prevent ignitions at an instant when the ignition angle is abnormally advanced, and to prevent the engine from being adversely affected by the ignition interruption operations.
Despite the desired prevention of excessive r.p.m. conducted by the system thus far described according to the proir art, however, operations are alternately effected by the ignition operations continuing for a certain period and by the misfiring operations resulting from the reliable interruptions of the ignition operations. As a result, the operational characteristics highly hunt so that high vibrations are caused in the vehicle driven by the engine. This invites a defect in that drivability and the comfortability are deteriorated, and also in that an abnormally abrupt and uncontrollable deceleration is caused by large-scale vibrations at the start of the ignition interrupting operations. Moreover, since a complete interruption of the ignition operation is conducted as the excessive r.p.m. preventing operation, there arises another defect in that a vehicle equipped with a tachometer for indicating engine r.p.m. on the basis of the signal at the drive termianl of the ignition coil will have its indicator jumping so highly as to make the driver anxious.